1. Field of the invention
The present invention is generally concerned with reading shapes.
It is more particularly directed to the situation in which a contact feeler is used to follow the shape to be read by applying the contact feeler to the article concerned and noting its coordinates at the relevant time.
2. Description of the prior art
This is the case in the published European patent No 291.378 which is more specifically directed to reading the contour of eyeglass frame rims or surrounds.
All contact feeler type contour reading devices currently known have the disadvantage that some force must be used to apply the contact feeler to the article concerned with the result that such application inevitably causes localized deformation of the article when it is a deformable article, as is often the case with eyeglass rims or surrounds, especially if the rims or surrounds are relatively thin and flexible.
The result is inaccurate reading of the contour.
What is more, in the case of reading the contour of eyeglass frame rims or surrounds the means that are necessarily employed to hold the eyeglass frame so that it does not move inevitably cause initial deformation of the rims or surrounds if they brace them laterally, as is usually the case.
This also results in inaccurate reading of the contour.
To avoid these problems shape reading devices have been proposed which use optical or pneumatic means and do not employ any contact feeler.
This is the case, for example, in the published European patent application No 226.349 and also in the German patent application No 38 14 697.
Without it being necessary to go into detail as to their implementation, suffice to say that these shape reading devices are characterized by their non-negligible intrinsic complexity.
They are therefore relatively costly.
Furthermore, there is sometimes doubt as to the focussing of their reading point, to the detriment of the required accuracy.
It is known to control accurately the force with which the contact feeler is applied to the article whose shape is to be read in a contact feeler type contour reading device, as in the European patent No 291.378 mentioned above.
A general object of the present invention is to exploit this possibility and utilize the deformation caused because the deformation in practise usually remains in the elastic range when the application force is relatively weak, as applies in the case of the more usual kinds of eyeglass frame rims or surrounds.